Question: The writing system of Urdu is based on which Arabic script based alphabet?
Paraphrase: The composing framework of Urdu is based on which Arabic script based alphabet?
SPARQL (Wikidata):  select distinct ?obj where { wd:Q1617 wdt:P282 ?obj . ?obj wdt:P31 wd:Q30016797 } 
Answer: Urdu alphabet